Hand-held ophthalmoscopes

ABSTRACT

A hand-held ophthalmoscope of exceedingly small dimensions capable of performing functions carried out by conventional ophthalmoscopes of much larger size. The ophthalmoscope includes a housing which carries an optical illuminating system. This latter system includes a light source as well as a lightdeflecting reflector or prism which directs the light toward the eye which is to be examined. A rotary lens wheel is carried by the housing for situating a selected one of a plurality of lenses along an observation path of the system so that when the operator looks through the selected lens he will see the background of the eye which is to be examined. The rotary lens wheel is transparent and has an inner surface directed toward the interior of the housing and an outer surface carrying indicia which identifies several lenses and is directed toward the operator. A lightconducting structure is situated in the interior of the housing to direct light from the light source to the rear of the transparent lens wheel so that this wheel will be illuminated even in the dark in order to render the indicia visible to the operator so that the operator will know which of the lenses is located at the observation path.

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[72] l Primary Examiner-David Schonberg m1- 1 e rse ng, gemil iil finztsy Assistant Examiner- Paul A. Sacher {21] Appl. No. 864,786Attorney-B1um, Moscovitz, Friedman and Kaplan [22] Filed Oct. 8, 1969[45] Patented Aug. 17, 1971 [73] Assignee Optotechnik G.m.b.H. andPropper Manufacturing Company, Inc. [32] Priority Nov. 23, 1968 I3 3]Germany [31] P18105361 SEARCH ROOM ABSTRACT: A hand-he1d ophthalmoscopeof exceedingly small dimensions capable of performing functions carriedout by conventional ophthalmoscopes of much larger size. Theophthalmoscope includes a housing which carries an optical i1-luminating system. This latter system includes a light source as H4]HANDHELD OPHTNMIMOSCOPES well us it light-deflecting reflector or prismwhich directs the light toward the eye which is to he examined. A rotarylens 12 Claims, 4 Drawlng Flgs. I l

. wheel 18 carried by the housing for situating a selected one ot'a [52]US. Cl. 351/12, plurality f lenses along an observation path of hesystem 50 351/16 7 that when the operator looks through the selectedlens he will [51] It'll. C1 A611) 3/12 see the background of the eyewhich is to be examined The [50) Field 01 Search 351/6, rotary lenswheel is transparent and has an inner Surface 9 l2 16 directed towardthe interior of the housing and an outer surface carrying indicia whichidentifies several lenses and is [56] Rderences cued directed toward theoperator. A light-conducting structure is UNITED STATES PATENTS situatedin the interior of the housing to direct light from the 1,791,604 2/1931Reardon 351/6 light source to the rear of the transparent lens wheel sothat 1,815,866 7/1931 Reese... 351/12 this wheel will be illuminatedeven in the dark in order to 3,0!9,699 2/1962 Schenk 351/12 render theindicia visible to the operator so that the operator 3,441,340 4/1969Moore et a1. 351/6X will know which of the lenses is located at theobservation 3,501,228 3/1970 Speelman 351/9 X path.

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. HELMUT A. HEiNE HAND-HELD OPHTHALMOSCOPES BACKGROUND OF THE INVENTIONThe present invention relates to ophthalmoscopes. Ophthalmoscopes areoptical instruments provided for observing the background of the livinghuman or animal eye.

Although ophthalmoscopes are well-known and widely used, they sufferfrom several drawbacks. Thus, in order to accomplish certain functionsit is essential that conventional ophthalmoscopes be of relatively largesize, rendering them inconvenient to handle and carry about as well asmaking them of an undesirably large weight Moreover, conventionalophthalmoscopes have certain conflicting requirements which enable themat best to perform according to a compromise between these requirements.a

The information which is derived from an ophthalmoscope with respect tothe condition ofthe background of the eye is of paiticular significanceto a physician not only in connection with diagnosing ailments of theeye but also very frequently in connection with diagnosing ailments ofother organs. As a result ophthalmoscopes are used not only inconsultation chamber of an eye specialist, but also it is frequentlynecessary to carry out examinations with bed-ridden patients who cannotcome to the consultation room in the office of the physician. Thus,internists, neurologists, surgeons and general practitioners oftenrequire a useful ophthalmoscope which will enable a rapid examination'ofthe background of the eye to be carried out.

Ophthalmoscopes have been known since the eye reflector was invented byH. Von Helmholtz. Exterior light sources which were initially used werereplaced by small electric.

lamps set into the instrument itself, and in the place of the relativelylarge flat or hollow reflector use was made of a small reflector or of asmall prism situated in the instrument. In order to compensate forrefraction abnormalities of the patient and/or ofthe physician, it hasbeen known for a long time to use corrective lenses situated, forexample, on a rotary lens wheel so that a selected lens could be locatedalong the light path used for making the observations of the eye whichis examined. Thus, all of the essential elements of an electricallyoperated hand-held ophthalmoscope are referred to above.

One of the important requirements of a good ophthal- I moscope is thatthe magnitude of the refractive power of the particular lens which issituated in the observation path be rendered conveniently visible evenin the dark since operations are frequently carried out with theophthalmoscope in a room which is fully or to a very large extent in adarkened condition.

It is known to utilize the light which is derived from a lamp of theinstrument not only for illumination of the background of the eye whichis examined, but also part of this light, particulnrly that whichtravels laterally from the lamp, is used for illuminating the lens wheelto indicate the above indicia with respect to the lenses. In the casewhere the lens wheel is transparent the light travels through the lenswheel. The forward or outer surface of the lens wheel carries thenumerals which indicate the required information with respect to thelens which is used. A magnifying lens is provided in a normal way tofacilitate reading ofthe illuminated number.

With a construction of the above type it is essential that the lamp besituated in front of that part of the lens wheel where the window atwhich the lens numbers are read is located, so that the informationdesired with respect to the particular lens which is located along theobservation path can be obtained easily even in the dark. However, thisrequirement necessitates a given size for the ophthalmoscope. Thus it isessential that the reflector or prism used for deflecting theilluminating light by approximately 90' be situated directly in front ofthe particular lens which is in the operative position along theobservation path. Since the parallax between the observation path andilluminating path should be maintained as small as possible, thearrangement of the light-deflecting reflector or between theilluminating lamp and the light-deflecting mirror or prism with theknown and currently used arrangements must be approximately the size ofthe diameter of the circle along which the several lenses of the lenswheel are located. A condenser is situated in front of the lamp and anaperture of suitable size is located in front of the condenser to besharply imaged at the background of the eye which is examined by way ofa suitable lens situated generally beneath the reflector or prism.

It is of course highly desirable to make the space between theaperture-imaging lens and the aperture itself sufficiently great toachieve sufficient brightness for the illumination provided by thebundle of light rays which illuminate the base of the eye. The reasonfor this requirement resides in the fact that the imaging of thefilament of the lamp must take place either in the pupil of the eye ofthe patient or at a location between the reflector or prism and the eyeof the patient, in order to achieve a satisfactory utility for theophthalmoscope.

In a situation where there is an extremely small distance between theaperture of the illuminating field and the imaging lens it is essentialthat the condenser also have an extremely small focal length so that theabove requirements with respect to the location of the image of the lampfilament be fulfilled while at the same time utilizing as great aspossible a part of the light issuing from the lamp for imaging the lampfilament so as to achieve a high degree of brightness for theilluminating bundle of light rays. However, the manufacture of comdenser lenses of relatively small focal length and sufficiently largediameter is limited for technical reasons. If, for example, as is oftenthe case with ophthalmoscopes, a hemispherical condenser is used, thenthe diameter thereof is equal to twice the radius of curvature of thecondenser. If the focal length is also to be maintained small, so as tofulfill the above requirements, then the diameter must also'bemaintained small, with the unavoidable result that there is a poor usemade of the light issuing from the lamp because the distance between thelamp filament and the first surface of the condenser cannot be reducedas much as desired because of the presence of the envelope of the lamp.As a result the opening angle within which the light issuing from thefilament of the lamp travels into the illuminating light path of theophthalmoscope remains relatively small.

It was first proposed to enlarge the diameter of the lens wheel so thatin this way, as described above, the maximum possible distance betweenthe illuminating objective and the condenser or lamp could be enlarged.However, this proposal resulted in an undesirable increase in the sizeof the ophthalmoscope since the enlarged lens wheel had to havesufficient space within the housing of the ophthalmoscope.

A further difficulty encountered in conventional ophthalmoscopes is thatthe optical components very often become SUMMARY OF THE INVENTION It isaccordingly a primary objective of the present invention to provide anophthalmoscope which will avoid all of the above drawbacks. I

above conflicting requirements but also can be manufactured at a sizeand weight much smaller than has heretofore been possible while at thesame time performing functions which could only be achieved from muchlarger ophthalmoscopes.

It is moreover an object of the invention to provide an ophthalmoscopewhich can easily and conveniently be carried about in a garment pocketduring visits of a physician to a hospital or the like.

Thus, it is an object of the invention to provide an ophthalmoscopewhich is exceedingly small, lightweight, while at the same timesufficiently robust to provide a long operating life.

It is furthermore an object of the invention to provide anophthalmoscope which will be well protected against soiling,particularly of the sensitive optical components without, however,requiring the inconvenient manipulations which might be necessary inconnection with placing the ophthalmoscope in a suitable case or thelike.

Furthermore, it is an object of the invention to provide anophthalmoscope which while capable of fulfilling all of the aboverequirements nevertheless will achieve a sufficiently great brightnessfor the purpose of examining the background of the eye, to achieve areliable result of the examination as well as to fulfill the mostimportant functions which heretofore could be achieved only byrelatively large ophthalmoscopes.

Thus, it is an object of the invention to provide an ophthalmoscopewhichpermits the indicia with respect to the particular selected lens tobe easily read even in the dark.

Also, it is an object of the invention to provide an ophthalmoscopewhich will be reliably protected against soiling, par tic ularly ofoptical elements.

Also, it is an. object of the invention to provide an ophthalmoscopewhich will enable a selected aperture or a selected filter to be locatedalong the optical axis of the optical system.

Furthermore, it is an object of the invention to provide anophthalmoscope which will enable the image of the aperture to be locatedeither at the background of the eye which is to be examined or at arelatively short distance from the ophthalmoscope.

In addition, it is an object of the invention to provide anophthalmoscope which makes it possible in a highly efficient manner torender the'blood vessels of the eye easily visible.

In accordance with the invention the ophthalmoscope in-' cludes ahousing which carries an optical illuminating system. This latter systemincludes a light source and a light-deflecting means for deflectinglight from the light source toward the eye which is to be examined. Alens wheel is supported for rotarymovement by the housing of theophthalmoscope, and this lens wheel carries a plurality of differentlenses one ofwhich is selected to be located along the observation pathalong which the physician will observe the condition of the eye which isexamined. This lens wheel is transparent and has an inner surfacedirected toward the interior of the housing and an outer surfacedirected toward the operator and carrying the indicia for the severallenses of the lens wheel. A light-directing means receives light fromthe light source and directs it to the rear or inner surface of thelenswheel so that the light travels through the transparent lens wheelto illuminate the indicia on the front or'outer surface thereof, thusrendering this indicia visible even in the dark.

BRIEF DESCRIPTION OF DRAWINGS The invention is Illustrated by way ofexample in the accom panying drawings which form part of thisapplication and in which:

FIG. 1 is a fragmentary sectional elevation of an ophthal- FIG. 3 is afragmentary partly sectional elevation of the ophthalmoscope as seen inFIG. 1 showing the ophthalmoscope as it appears from the exterior exceptfor the illustration in section of a detent means to be used for thelens wheel; and

FIG. 4 is a perspective illustration of the light-directing means of theophthalmoscopeof the invention.

DESCRIPTION OF A PREFERRED EMBODIMENT Referring to FIG. 1, the filamenttype ofincandescent lamp 1 forms a light source from which light issuesto be collected by the condenser 2, when the lamp 1 is energized. Thelight which is thus concentrated by condenser 2 passes through anilluminating field aperture 9' and, in the illustrated example, a filter9 which, for example, is a red free filter so that in this way it ispossible to render the blood vessels atthe retina more easily visible.The optical system includes, in addition to the above elements anobjective 29 which images the illuminating field aperture sharply at apredetermined distance ahead of the ophthalmoscope. Preferably arelatively large imaging distance is selected such as, infinity forexample, so that with a patient having emmetropia, it is possible toachieve a sharp image of the illuminating field aperture at the base ofthe eye.

The optical system further includes a light-deflecting means which inthe illustrated example is a reflector 30 which deflects theilluminating bundle of light rays through an angle of 90 forwardly totli'e eyewlii'ch is examined. The operator looks into the ophthalmoscopethrough an inlet opening covered by a transparent flat disc 21 situatedwithin and closing the observation aperture. This aperture andtransparent cover 21 are located along an observation path which extendsover the upper edge of the reflector 30 toward the eye of the patient.In this way it is possible to achieve the smallest extent of parallaxbetween the illuminating path and observation path. The housing 17,20 ofthe ophthalmoscope carries not only the above-described optical systembut also a rotary lens wheel 14 which is transparent and carries aplurality of lenses 23 a selected one of which is situated along theobservation path in alignment with the transparent plate 21, asindicated in FIG. I. The selected lens 23 of the lens wheel 14 serves tocompensate for refraction abnormalities in the eye of the patient and/orin the eye of the examining physician, while at the same time it ispossible with this construction to determine the magnitude of elevationsat the base of the patients eye.

The entire optical and mechanical structure of the ophthalmoscope arecarried by the housing 17,20 which includes the primary housingcomponent 20 and the front component 17 connected to the component 20 toform the ophthalmoscope housing therewith. The entire ophthalmoscope ismounted on a hollow handle 27, with a threaded connection being providedbetween the ophthalmoscope and handle in the illustrated example. Thehandle 27 accommodates batteries 28 in its interior, these batteriessupplying the energy for the lamp 1. Also the handle 27 carries amanually operable switch 31, in the form ofa shiftable switch. Throughactuation of this switch the lamp 1 is energized and deenergized.

As explained above, it is required that the illuminating objective 29have a sufficiently great distance ahead of the lamp 1 or the condenser2, so as to bring about in this way an optical utility of the lightissuing from the lamp. The lens wheel 14 is, however, with theinstrument of the invention, maintained at an extremely small size, soas to assure small dimensions for the entire ophthalmoscope. Thenumerals which indicate the refractive power of the particular lens 23which is aligned with the observation path are engraved on the outerright side of the lens wheel 14 as viewed in FIG. 1. Thus, at the regionl5 there will be numerals diametrically opposed from the particular lens23 at the observation path indicating the refractive power of the lens23 at the observation path. These numerals can also be printed orotherwise situated at the outer surface of the lens wheel I4, thusforming an identifying indicia for the lenses carried by the wheel 14.

A direct illumination of the lens wheel by the lamp 1 is not possiblebecause the lamp 1 is situated too far away from the lens wheel 14. Inaccordance with the invention, therefore, there is provided laterally ofthe lamp 1 a light-conducting means in the form of a light-conductingbar 4 made ofa suitable material, such as, for example, lucite or otheracryllic glass having the property of conducting light along theinterior of the body from one end to the other end thereof withoutescape of light from the side surface of the body. Thus, thelight-conducting means includes the light-conductive rod or bar 4, shownmost clearly in FIG. 4, and provided with the inclined end surfaces 5and 6 which respectively receive the light from the lamp and dischargethe light, this light issuing from the surface 6. These end surfaces 5and 6 may have an angle of 45, for example, with respect to the axis ofthe rod 4. The light which issues laterally from the lamp 1 is thusreceived at the surface 5 and flows along the interior of the rod 4 toissue from the upper end surface 6 thereof. This upper end surface 6 issituated in an interior chamber of the housing which also receives thelower portion of the transparent wheel I4 at the elevation of theindicia corresponding to the upper selected lens 23, so that in this waythe light from the lamp is directed through the wheel 14 to illuminatethe indicia on the outer surface of the wheel 14. The light which issuesfrom the end 6 of the light-conducting means passes through thetransparent.

wheel 14 from the inner surface thereof which is directed toward theinterior of the housing to the outer surface thereof so as to render thelndicia l5 visible even in the dark. In order to facilitate reading ofthe indicia a magnifying lens I6 can be carried by the housing at theopening thereof through which the indicia 15 becomes visible.

in this way the structure of the invention enables the distance oftheilluminating objective 29 from the condenser 2 or the lamp 1 to becompletely independent of the diameter of the lens wheel I4. At the sametime, a good illumination ofthe indicia on the lens wheel is assuredsince the light-conducting rod 4 can have any desired length.

Furthermore, in accordance with the invention the rod 4 serves as ashaft extending through an aperture wheel 7 to serve as a shaftsupporting the aperture wheel7 for rotary movement about an axisparallel to the optical axis, the rod 4 of course extending parallel tothe optical axis. In addition the I rod4 forms a single unitary bodywith the holder for the condenser 2. This result is achieved withoutdifficulty when the holder for the condenser and rod 4 are both made inone piece by injection molding, using a transparent, 'clear, uncoloredplastic having the appearance of transparent glass, for exampie. Thus,the unit shown in FIG. 4 may be case or injection molded in oneoperation and in one piece and includes the rod 4 with its inclined ends5 and 6 as well as the holder 3 for the condenser 2. This holder 3 is asimple cylindrical body integral with and extending laterally from therod 4 and formed with -an axial bore whose axis coincides with theoptical axis. The

condenser 2 may be mounted directly in the axial bore of the holder 3 orthe condenser 2 may be situated within a metal mounting ring 2' which issituated within the holder 3, as illustratcd in FIG. 1. Thus, thestructure of FIG. 4 which serves not only as a light-conducting means,as a support for the rotary movement of the aperture wheel, and as aholder for the condenser is highly favorable from an economicstandpoint, per milling the ophthalmoscope to be manufactured and soldat highly favorable prices, but in addition with this construction it ispossible to locate the aperture wheel 7, with respect to the axis of thecondenser, with the smallest possible number of dimension tolerances inthe most precise manner within the entire assembly so that the greatestpossible accuracy is achieved at the lowest possible cost.

The structure of the inventionincludes a detent means for releasablyretaining the aperture wheel 7 at a selected angular position. and theconstructive principle used for the detent means which coacts with theaperture wheel is also used for a detent means which coacts with thelens wheel 14 for maintaining the later precisely at a preselectedangular position.

Thus, referring to FIG. 3, it will be seen that the detent means whichcoacts with the lens wheel 14 includes a part of the front housingportion 17 formed with a bore 24 which receives a spring 25 of thedetent means. This spring 25 presses a ball 26 of the detent means intoa bore 22 of the lens wheel 14. This lens wheel 14 is provided with theseveral bores 22 angularly distributed along a given circle around theaxis of the lens wheel and respectively accommodating the lenses 23 intheir interiors. Thus, each of the bores of the lens wheel whichreceives a lens 23 also acts as a recess for receiving the springpressedball of the detent means. In this way it is possible to achieve anextremely high accuracy in the positioning of the lens wheel with thisreleasable detent means. This feature is of considerable significance inorder to have the assurance that parallax between the illuminating andobservation paths is maintained as small as possible with the selectedlens 23 being situated so that it is fully operative without anypossible undesirable covering of the selected lens 23 by the primaryhousing component 20 at the observation window thereof where the flattransparent closure plate 21 is provided.

Inasmuch as the ophthalmoscope should have a number of differentilluminating field apertures in order to fulfill its purposes withoutany limitations, the aperture wheel 7 is provided with a plurality ofilluminating field apertures at one or more of which it is possible tolocate color filters. In the particular example which is illustrated inFIG. I there are four illuminating field apertures of which two arevisible in the drawing while the other two are situated ahead of andbehind the plane of FIG. 1. These illuminating field apertures can be inthe form of circular apertures of different diameters or they can takethe form of elongated gap-type of apertures so that is is possible toprovide gap or slit illumination with the ophthalmoscopc. It is alsopossible to provide apertures of semicircular configuration to achieve agood operation of the ophthalmoscope because of the reduction ofreflection from the cornea of the patient particularly where the pupilhas not been enlarged. It is also possible to utilize color filters,particularly red-free filters; so as to provide a better visibility forthe blood vessels. In FIG. 1 the filter 9 is shown in an operativeposition along the optical axis of the illuminating system.

In order to be able to locate the aperture wheel 7, even through the rod4 extends through a centraljournal thereof, in a precisely determinedangular position properly aligning the illuminating field aperture withthe condenser 2, the structure of the invention also includes thefeature according to which the axis of therod 4 coincides with the axisof the wheel 7. Only with such an arrangement does it become possible tomaintain the entire assembly as compact as possible so as to occupy thesmallest possible space while at the same time having a relatively largenumber of illuminating field apertures from which a selection ofaparticular aperture can be made, and while at the same time achieving agood illumination of the indica on the lens wheel in the mannerdescribed above.

With an ophthalmoscope it is highly desirable to have available not onlya relatively small aperture for the bundle of light rays, as whenoperating the ophthalmoscopc with a pupil which has not been widened,particularly when examining macula lutea, but also it is desirable tohave available a relatively large aperture for the illuminatinglight-rays so that it is possible to simultaneously illuminate thelargest area of the retina with a widened pupil. For these reasons it isdesirable to make one of the apertures as large as possible. The largestpossible illuminating field aperture, or the largest diameter thereof,is determined by the largest permissible opening of the condenser 2.Thus, it is desired to make the diameter of the illuminating fieldaperture of largest size as equal as possible or only slightly smallerthan the effective condenser aperture. For these reasons it is requiredthat the illuminating ficld aperture of largest size be centered asaccurately as possible with respect to the optical axis of the condenser2. This of course results in a requirement that the aperture wheel 7 beprovided with an extremely accurate detent structure or the like todetermine the angular position of the wheel 7, so as to assure that theapertures will always return reliably to precisely the same locationssituated exactly along the optical axis even when there is a frequentactuation of the aperture wheel, so as to guarantee that each aperturewill have its center situated precisely in the optical axis of thecondenser.

In accordance with the invention this structure is achieved, in themanner illustrated in FIG. 2., with a detent means which includes thespring pressed ball 11 received in a bore 12 of the front housingcomponent 17 and urged by spring 13 downwardly against the aperturewheel 7. In this way the openings of the aperture wheel 7 which serve toaccommodate the illuminating field apertures serve at the same time asdetent recesses to receive the spring-pressed detent ball 11. FIG. 2illustrates how the spring 13 urges the detent ball 1 1 into the boreofthe wheel 7. Also it is apparent from FIG. 2 that the illuminatingfield aperture 8 is accommodated in the lower region of the opening 10beneath the ball 11, Thus, by providing openings which simultaneouslyserve as detent recesses the greatest possible accuracy in the angularpositioning of the aperture wheel is assured. In this way the diameterof the largest image field aperture can approach the size of theeffective diameter of the condenser with only small accuracy tolerancesbeing required.

The soiling of an ophthalmoscope by depositions of dust or condensing ofvapors onto components is a problem which is frequently encountered. Inparticular the lenses of the lens wheel are subjected to this problembecause with most of the known ophthalmoscopes the dust has access tothe ophthalmoscope from the front and rear sides thereof. The dust caneasily enter into the ophthalmoscope through the generally openobservation aperture directed toward the eye of the operator so as tobecome deposited on the lenses of the lens wheel, and it is alsopossible for the dust to enter through the exit window of the light tosettle on the other side of the lenses. Inasmuch as many operators ofophthalmoscopes begin the operation with a lens of predeterminedrefractive power corresponding to the refraction error of the particularoperator, so that when the ophthalmoscope is not used it is almostalways this particular lens which is in the operating position in frontof the observation window, it is precisely this one lens which receivesdust deposits to such an extent that it becomes no longer possible tolook through lens. Then the ophthal-,

rnoscope must be submitted for repairs, since cleaning of the small lensin the interior of the ophthalmoscope cannot be carried out by theoperator of the ophthalmoscope.

Through both of the above openings in the housing of the ophthalmoscopeit is possible not only to expose the lens wheel to soiling by dustdeposits and the like but also other elements of the illuminating systemare subjected to this undesirable phenomenon. In particular dustdeposits which settle on the condenser lenses, the illuminating fieldapertures, and filters located at the latter apertures form a particularsource of trouble because each particle of dust becomes'imaged to astrongly enlarged extent in the illuminating field of the ophthalmoscopeand thus brings about particularly harmful effects in the operation ofthe ophthalmoscope.

It is therefore proposed in accordance with the invention to takecertain constructive measures which will to a very great extent preventany soiling of the instrument when it is used. In accordance with theinvention the exit window 19 for the light is closed when the instrumentis not used by a dusttight protective cover. This dusttight protectivecover is, in accordance with the invention, a component of theinstrument of the invention and is movable either by swinging, turning,or shifting so as to be displaced to a covering position closing thelightexit window 19. In the example illustrated in FIG. 1 the dusttightprotective cover is in the form of a shiftable slide 18, which, when theophthalmoscope is not used, is shifted to a closed position closing theexit window 19. In FIG. 1 the cover slide 18 is shown in its closedposition while in FIG. 2 it is shown in an open position. The slidablecover 18 of the invention is preferably made of a transparent materialof conspicuous color such as red, for example, any suitable plasticbeing used for this purpose. In this way the operator will'immediatelyknow that the exit window is covered by the slide 18 when the operatorlooks into the ophthalmoscope, so that it is not possible to erroneouslyoperate the ophthalmoscope with the cover 18 in its closed position. Theslide 18 will remain in any position it is shifted to be'reason of itsfrictional engagement with the housing component 17. At its lowerportion the slide 18 is provided with a raised part 18' havingtransversely extending teeth accessible to a finger of the operator, asis clearly apparent from FIGS. 1 and 2, so that simply by touching theexterior teeth at the raised part ofthe slide 18 the operator canmanually shift the slide 18 to any desired position, such as either ofthe positions shown in FIGS. 1 and 2, respectively, without smudging orotherwise detracting from the effectiveness of the upper portion of theslide 18.

In order to also protect the observation opening against entrance ofdust or other deposits into the interior of the ophthalmoscope thisobservation opening is closed by the flat glass disc 21. Since theexterior surface of this disc 21 will of course receive deposits ofdust, it is situated in such a way that this exterior surface of thecover 21 can be easily cleaned without any difficulty. However, in orderto protect this cover 21 from scratching or other injury, as would bethe case if the exterior surface of the cover 21 were situated at oroutwardly beyond the exterior surface of the housing component 20, thishousing 20 is formed with a frustoconical depression leading to theobservation aperture which is closed by the plate 21 and having such asize that while easy cleaning of the plate 21 is possible neverthelessthe plate 21 is sufficiently recessed to be protected against scratchingor other injury.

With the particular construction of the invention as described above itis hardly possible for the aperture wheel or the apertures and filterscarried thereby to become soiled with dust deposits or the like becauseof the highly protective arrangement of these components in theassembly, nevertheless the structure of the invention takes suitablemeasures in this connection also to prevent entry of dust and the intothe opthalmoscope at the location of the aperture wheel. For thispurpose a spring ring 33 (FIG. 1) having a suitably dishedconfiguration, presses a sealing ring 32 upwardly against the aperturewheel 7. At the same time the aperture wheel itself is pressed against adownwardly directed stop surface of the front housing component 17, sothat neither the upper side nor the lower side of the aperture wheelwill permit dust to enter. This is of particular significance becauseeven an extremely small amount of dust at the edges of the apertures orat the filters become readily noticed in a most unpleasant manner sincethe illuminating field apertures are imaged in a greatly enlarged mannerby the illuminating objective 29. The above-described dust-protectingstructure at the aperture wheel increases, thus, the extent to which theophthalmoscope of the invention will provide valuable use.

According to a particular embodiment of the invention the slide 18 isconstructed in such a way that that part thereof which in the closedposition of the slide is situated in front of the light-exit window ismade of a transparent material having flat, parallel opposed surfaces.In particular, the arrangement is such that the slide 18 is made of atransparent green plastic having a spectral absorption designedparticularly to prevent red light from passing through. With a suitablethickness for the upper part of the slide 18 it is then possible tooperate the ophthalmoscope with the slide 18 in its closed position, sothat now the slide 18 will function not only to protect against theentry of dust but also as a green or red-free filter, or as a filter ofanother color such as a blue filter to be used in fluorescent operationsof the ophthalmoscope. In this case it is not necessary to provide inone of the possible angular positions of the aperture wheel 7 a colorfilter to be situated along the optical axis, so that instead it ispossible to have an additional illuminating field aperture such as, forexample, an aperture of extremely small diameter.

Since the plane in which the slide 18 is located is situated at an anglesubstantially different from with respect to the direction of the lightbundle issuing from the instrument through the window 19, and since theobservation path extends also parallel to the direction of travel of thelight through the window 19 toward the eye, undesirable reflections atthe surfaces of the cover 18, which would greatly detract fromtheeffec'liveness of the operation, are reliably excluded with thefilter which also serves as the dusttight protective closure. If thefilter formed by the cover 18 did indeed extend approximatelyperpendicularly to the path oflight travel and the observation path,then because of the strong reflection at both surfaces of such adust-protecting slide in its closed position it would hardly be possibleto make any use of the instrument whatsoever. The arrangement of theinvention according to which the dust-protecting slide is situated at asubstantial angle different from 90 with respect to the path oflighttravel and path of observation makes it possible to use the slide 18also as a filter.

According to a further modification of the concept of the invention itis also possible to provide at that part of the slide 18 through whichthe bundle of light travels after being reflected by the reflector 30 ora prism equivalent thereto, a positive or collecting lens of suitablerefractive power. With such a construction the image of the illuminatingfield aperture will not be located at a relatively great distance fromthe ophthalmoscope but instead can be situated at a relatively shortdistance in front of the opthalmoscope in accordance with the particularfocal length of the lens which is carried by and forms part of the cover18 with such a construction. The focal length of this lens is selectedin such a way that the image of the aperture is located approximately30-40 mm. in front of the ophthahnoscope. The resulting aperture imageis, corresponding to the short imaging distance, small and thus verybright. Within the aperture wheel 7 there are provided, among the otherapertures, as pointed out above, slit-shaped apertures. The very brightimage of such slit apertures, provided with a positive lens of the abovetype carried by and forming part of the dust cover 18, is highlysuitable for use of the ophthalmoscope as a hand-held lamp and providesthe instrument with an even more universal utility. Thus, with thisparticular embodiment of the invention the cover slide 18 preferably ismade not of a colored plastic but rather of a colorless clear glass typeof plastic. The positive lens which thus is carried by and forms part ofthe cover slide 18 may be injection molded in one piece with remainderofthe slide 18.

The entire ophthalmoscope is mounted on the battery or cable holdinghandle, being threaded thereto as shown at 27' in the example of FIG. 1.The hollow handle can, if desired, receive suitable dry cell type ofbatteries or rechargeable cells. in correspondence with the smalldimensions of the entire ophthalmoscope, small dimensions are alsoprovided for these batteries. The handle which accommodates thebatteries also carries the switch mechanism for tuning the lamp 1 on andoff.

Thus, with all or part of the above-described features of the inventionit becomes possible to provide an exceedingly small ophthalmoscopehaving operating capabilities of the highest optical quality and capableof carrying out the most important functions which heretofore could onlybe carried out by much large instruments.

What I claim is:

1. In a hand-hcld ophthalmoscope, a housing having a hollow interior, anoptical illuminating system carried by said housing in the interiorthereof and including a light source and a light-deflecting means fordirecting light along an optical axis of said illuminating system fromthe light source toward an eye which is to be viewed, an observationsystem also carried by said housing and including a rotary lens wheelcarrying a plurality of lenses for situating a selected lens along anobservation light path of the observation system at that part thereofthrough which the operator observes the eye, said rotary lens wheelbeing supported for rotary movement by said housing and being made of atransparent material provided with an inner surface directed toward andcommunicating with the interior of the housing at an interior portionthereof which is axially displaced along said optical axis from saidlight source between the latter and said light-deflecting means and saidrotary lens wheel having an outer surface directed outwardly toward theoperator and carrying indicia for respectively indicating which of thelenses of the lens wheel is in an operative position at the observationpath, and light-conducting means situated entirely in the interior ofsaid housing and being spaced in its entirety radially beyond saidoptical axis and extending parallel to said optical axis from a locationsituated beside said light source to a location communicating with saidinterior portion of said housing with which said inner surface ofsaidrotary lens wheel communicates for receiving light radiating radiallyfrom said light source and for conducting the received light along apath spaced radially beyond and extending parallel to said optical axisinto said interior portion of said housing to illuminate said innersurface of said transparent lens wheel for directing through the latterlight which illuminates the indicia even in the dark, so that theoperator knows which of the lenses has been located at the observationpath.

2. The combination of claim 1 and wherein a rotary aperture wheel isrotatable at least partly within said housing and has an axis ofrotation extending parallel to the optical axis of the opticalilluminating system, said aperture wheel being formed with openingsextending therethrough parallel to its axis of rotation and formingapertures one of which may be selected to be situated along the opticalaxis, and detent means coacting with said aperture wheel for releasablymaintaining the latter at a selected angular position, said detent meansincluding a spring-pressed ball urged into one of said openings of saidwheel so that said openings function not only to accommodate exposureapertures but also as part of the detent structure for releasablysituating a selected aperture at the optical axis.

3. The combination of claim 2 and wherein at least one filter issupported in one ofsaid openings ofsaid aperture wheel.

4. The combination of claim I and wherein said lens wheel is formed withopenings which respectively receive different lenses, and aspring-pressed ball carried by said housing and urged into a selectedone of said openings for releasably holding said lens wheel at aselected angular position, whereby the openings of said lens wheel whichreceives said lenses also function as part of the detent structure forreleasably holding the lens wheel at a selected position.

5. The combination of claim 1 and wherein said housing has an exitwindow through which light travels from the housing toward an eye whichis to be examined, and slidable closure means shiftably carried by saidhousing for closing and opening said window to prevent dust fromentering through the latter window when the ophthalmoscope is not used.

6. The combination of claim I and wherein said housing has anobservation opening through which the operator looks into said housingalong said observation path, and said housing carrying in saidobservation opening a transparent plate which prevents dust fromentering into said housing through said observation opening thereof, thelatter opening having a frustoconical configuration and terminating atan outer surface of said housing which is directed toward the operatorand which is situated beyond said transparent plate by a distancesufficient to enable the latter to be conveniently cleaned whileprotecting said transparent plate from being scratched or otherwiseinjured.

7. The combination of claim 1 and wherein a hollow handle is releasablyfixed to and carries said housing, said handle accommodating in itsinterior batteries for supplying electrical energy to said light sourceand said handle also carrying a manually operable switch for closing andopening the circuit between batteries and said'light source.

8. The combination of claim 1 and wherein a rotary aperture wheel isrotatable at least partly within said housing and has an axis ofrotation extending parallel to the optical axis of the opticalilluminating system, said aperture wheel being formed with openingsextending therethrough parallel to its axis of rotation and formingapertures one of which may be selected to be situated along the opticalaxis, said light-conducting means including an'elongatedlight-conducting bar which extends parallel to said optical axis fromthe location besides said light source to said interior portion of saidhousing, said bar extending through said aperture wheel centrally of helatter and functioning also as a shaft on which said aperture wheel issupported for rotary movement.

9. The combination of claim 8 and wherein said system also includes acondenser, said light-conducting means having a portion forming a holderfor said condenser.

10. The combination of claim and wherein said slide is made of atransparent, colored plastic and is shiftable in a

1. In a hand-held ophthalmoscope, a housing having a hollow interior, anoptical illuminating system carried by said housing in the interiorthereof and including a light source and a lightdeflecting means fordirecting light along an optical axis of said illuminating system fromthe light source toward an eye which is to be viewed, an observationsystem also carried by said housing and including a rotary lens wheelcarrying a plurality of lenses for situating a selected lens along anobservation light path of the observation system at that part thereofthrough which the operator observes the eye, said rotary lens wheelbeing supported for rotary movement by said housing and being made of atransparent material provided with an inner surface directed toward andcommunicating with the interior of the housing at an interior portionthereof which is axially displaced along said optical axis from saidlight source between the latter and said light-deflecting means and saidrotary lens wheel having an outer surface directed outwardly toward theoperator and carrying indicia for respectively indicating which of thelenses of the lens wheel is in an operative position at the observationpath, and light-conducting means situated entirely in the interior ofsaid housing and being spaced in its entirety radially beyond saidoptical axis and extending parallel to said optical axis from a locationsituated beside said light source to a location communicating with saidinterior portion of said housing with which said inner surface of saidrotary lens wheel communicates for receiving light radiating radiallyfrom said light source and for conducting the received light along apath spaced radially beyond and extending parallel to said optical axisinto said interior portion of said housing to illuminate said innersurface of said transparent lens wheel for directing through the latterlight which illuminates the indicia even in the dark, so that theoperator knows which of the lenses has been located at the observationpath.
 2. The combination of claim 1 and wherein a rotary aperture wheelis rotatable at least partly within said housing and has an axis ofrotation extending parallel to the optical axis of the opticalilluminating system, said aperture wheel being formed with openingsextending therethrough parallel to its axis of rotation and formingapertures one of which may be selected to be situated along the opticalaxis, and detent means coacting with said aperture wheel for releasablymaintaining the latter at a selected angular position, said detent meansincluding a spring-pressed ball urged into one of said openings of saidwheel so that said openings function not only to accommodate exposureapertures but also as part of the detent structure for releasablysituating a selected aperture at the optical axis.
 3. The combination ofclaim 2 and wherein at least one filter is supported in one of saidopenings of said aperture wheel.
 4. The combination of claim 1 andwherein said lens wheel is formed with openings which respectivelyreceive different lenses, and a spring-pressed ball carried by saidhousing and urged into a selected one of said openings for releasablyholding said lens wheel at a selected angular position, whereby theopenings of said lens wheel which receives said lenses also function aspart of the detent structure for releasably holding the lens wheel at aselected position.
 5. The combination of claim 1 and wherein saidhousing has an exit window through which light travels from the housingtoward an eye which is to be examined, and slidable closure meansshiftably carried by said housing for closing and opening said window toprevent dust from entering through the latter window when theophthalmoscope is not used.
 6. The combination of claim 1 and whereinsaid housing has an observation opening through which the operator looksinto said housing along said observation path, and said housing carryingin said observation opening a transparent plate which prevents dust fromentering into said housing through said observation opening thereof, thelatter opening having a frustoconical configUration and terminating atan outer surface of said housing which is directed toward the operatorand which is situated beyond said transparent plate by a distancesufficient to enable the latter to be conveniently cleaned whileprotecting said transparent plate from being scratched or otherwiseinjured.
 7. The combination of claim 1 and wherein a hollow handle isreleasably fixed to and carries said housing, said handle accommodatingin its interior batteries for supplying electrical energy to said lightsource and said handle also carrying a manually operable switch forclosing and opening the circuit between batteries and said light source.8. The combination of claim 1 and wherein a rotary aperture wheel isrotatable at least partly within said housing and has an axis ofrotation extending parallel to the optical axis of the opticalilluminating system, said aperture wheel being formed with openingsextending therethrough parallel to its axis of rotation and formingapertures one of which may be selected to be situated along the opticalaxis, said light-conducting means including an elongatedlight-conducting bar which extends parallel to said optical axis fromthe location besides said light source to said interior portion of saidhousing, said bar extending through said aperture wheel centrally of thelatter and functioning also as a shaft on which said aperture wheel issupported for rotary movement.
 9. The combination of claim 8 and whereinsaid system also includes a condenser, said light-conducting meanshaving a portion forming a holder for said condenser.
 10. Thecombination of claim 5 and wherein said slide is made of a transparent,colored plastic and is shiftable in a plane extending angularly acrosslight issuing through said exit window at an angle which issubstantially different from an angle of 90*.
 11. The combination ofclaim 10 and wherein said slide is green.
 12. The combination of claim 5and wherein said slide carries a positive lens situated in the path oflight rays passing through said exit window when said slide is in aclosed position covering said window so that positive lens will situatean image closer to the opthalmoscope than when the light rays passthrough the open exit window.